The first representatives of the genus Rhabdomastix (Diptera, Limoniide) with extremely long antennae (much longer than the body) is discovered in the fossil record. The paper presents new data on Eocene species of the genus Rhabdomastix including a new species with surprisingly long and tiny antennae with characteristic almost black spots on individual flagellomeres from Bitterfeld amber: Rhabdomastix (Rhabdomastix) woottoni sp. nov. Two other species have been discovered and described based on inclusions in Baltic amber: Rhabdomastix (Rhabdomastix) setosa sp. nov. and Rhabdomastix (Rhabdomastix) rafali sp. nov. Antennae with similar morphology are characteristic for the American Recent species collectively known as “Rhabdomastix illudens”. New nomenclature decisions include a transfer of three species from Baltic amber with antenna longer than the body to the subgenus Rhabdomastix. These species: Rhabdomastix ( Rhabdomastix) grussica Podenas, 2006 comb. nov., Rhabdomastix ( Rhabdomastix) mastix Podenas, 2006 comb. nov. and Rhabdomastix (Rhabdomastix) setix Podenas, 2006 comb. nov., were not previously classified to any subgenus. New discovery of a species of Rhabdomastix with extremely elongate, very narrow antennae, sheds new light on the evolutionary history of this genus. The paper also presents interpretations of the ecological preferences of some modern representatives of the genus and their Eocene ancestors.

Key words: Insecta, Diptera, Limoniide, inclusions, taxonomy, evolution, Baltic amber, Bitterfeld amber, Eocene.

Wiktoria Jordan-Stasiło [wjordan@ur.edu.pl; ORCID: https://orcid.org/0000-0001-5621-6917] and Iwona Kania-Kłosok [ikania@ur.edu.pl; ORCID: https://orcid.org/0000-0002-2325-4308] (corresponding author), Institute of Biology, University of Rzeszów, Zelwerowicza 4, 35-601 Rzeszów, Poland. Wiesław Krzemiński [wieslawk4@gmail.com; ORCID: https://orcid.org/0000-0001-5685-891X], Institute of Systematics and Evolution of Animals, Polish Academy of Sciences, Sławkowska 17, 31-016 Kraków, Poland.